Semiconductor memory devices are used extensively to store data. Memory devices can be characterized according to two general types: volatile and non-volatile. Volatile memory devices such as static random access memory (SRAM) and dynamic random access memory (DRAM) lose data that is stored therein when power is not continuously supplied thereto.
Non-volatile memory devices, such as flash erasable programmable read only memory (Flash EPROM) devices, retain stored data even in the absence of power supplied thereto. Unfortunately, non-volatile memory devices typically operate more slowly than volatile memory devices. For example, a Flash EPROM device write access time is in the range of microseconds to milliseconds, while the SRAM or DRAM write access time is in the range of picoseconds to nanoseconds.
Accordingly, it would be desirable to provide a universal type memory device that includes the advantages of both volatile and non-volatile memory devices, i.e., fast operation on par with volatile memories, while having the ability to retain stored data when power is discontinued to the memory device.
It would further be desirable to provide such a universal type memory device having a size that is not prohibitively larger than comparable volatile or non-volatile devices.